Engineering Drought-Responsive ABA Signaling: Linking Physiological Stress Cues to Metal–Organic Framework-Mediated ABA Delivery and SnRK2 Activation

Drought induces coordinated physiological, biochemical, and molecular responses that extend beyond changes in phytohormone concentrations. Rapid alterations in reactive oxygen species (ROS), apoplastic pH, Ca2+ and ionic dynamics, tissue hydration, and cellular redox status provide spatial and temporal information on developing water deficit and regulate stomatal behavior, photosynthesis, water relations, and stress-responsive gene expression. This review explores whether endogenous drought-associated signals can serve as biological triggers for stimulus-responsive metal–organic frameworks (MOFs) designed to regulate abscisic acid (ABA) delivery. We integrate drought-induced changes in redox state, apoplastic pH, ionic composition, and hydration with MOF transformation, host–guest interactions, ABA release, uptake, transport, metabolism, and engagement of the PYR/PYL/RCAR–PP2C–SnRK2 signaling pathway. We propose a framework in which responsive MOFs generate a temporally controlled ABA pulse that follows drought progression, activates protective signaling during water limitation, and attenuates after rewatering to facilitate recovery. Particular emphasis is placed on ROS-Ca2+ crosstalk, SnRK2/OST1-dependent guard-cell regulation, hydraulic adjustment, photosynthetic protection, and recovery dynamics. Current studies demonstrate MOF-mediated phytohormone protection, controlled release, and drought-related physiological improvement. Current advances have established the feasibility of MOF-based ABA protection and controlled delivery; however, the integration of drought-responsive carrier activation with receptor-accessible ABA delivery and PYR/PYL/RCAR–PP2C–SnRK2 pathway validation remains an emerging research frontier. We therefore outline a claim-matched validation framework integrating spatial drought-signal analysis, isotope-resolved ABA tracing, carrier localization, phosphorylation-based pathway assays, drought–rewatering experiments, and physiological assessment. This integration of plant stress physiology with responsive nanomaterials provides a conceptual basis for developing more precise ABA delivery strategies for crop resilience under increasingly variable water availability.